Greensboro, Md. — Officials have released body camera video of a deadly encounter between police and a black teenager who died after struggling with officers in a town on Maryland's Eastern Shore, footage that fueled a civil rights group's call for an independent investigation.

Greensboro Police Chief Mike Petyo released the footage after a county prosecutor announced Thursday that he isn't asking a grand jury to consider criminal charges in the September 2018 death of 19-year-old Anton Black.

The video shows Black's mother screaming after police chased her son to the driveway of his family's home, where an officer smashed a car window to get to Black inside and then shocked him with a stun gun before the teen struggled with three officers and a civilian. The footage also captured how Black's mother and officers reacted when they realized he stopped responding.

Caroline County State's Attorney Joseph Riley said in a statement that his office "is not empowered to prosecute tragic acts." An autopsy report, signed Wednesday by the state's chief medical examiner, says Black suffered "sudden cardiac death." It said a congenital heart condition, mental illness, and stress from the struggle likely contributed to his death.

Lawyers for Black's family vowed Thursday to ask the U.S. Justice Department's civil rights division to investigate his death. The American Civil Liberties Union of Maryland joined their call for a federal investigation or an independent investigation by the governor-appointed Maryland State Prosecutor, whose office investigates misconduct in office by public officials or employees.

The group said in a statement Friday that the "disturbing" video shows officers used excessive force on a man who shouldn't have been arrested. Family attorneys said in a statement Black committed no crime and there was no reason for Webster and the other officers from neighboring departments to chase him back to his home, no reason for Webster to break the car's window, and no reason to Tase the teen or restrain him.

"There was no reason for Anton Black to die," the statement said.

It says the family only Wednesday received the autopsy report, though it was completed a day after his death.

"The ACLU is outraged by the gross delay in the handling and release of information related to the autopsy and police body camera footage, which raises significant red flags that local law enforcement agencies have something to hide in Anton's death," the statement says.

Family attorneys had urged Riley to convene a grand jury for the investigation. They claim police used excessive force on the teen and argue the autopsy report mischaracterizes his death as accidental.

The attorneys said in a statement the autopsy notes 43 abrasions, contusions or hemorrhages they say Black suffered during the struggle with officers.

Anton Black
LaToya Holley via AP

"The autopsy raises serious questions about why such a high degree of force was used on an unarmed teenager on his own property who posed no threat to law enforcement or the public," Timothy Maloney, one of the family lawyers, wrote in an email Thursday.

The encounter began when Greensboro Police Department officer Thomas Webster IV responded to a 911 call from a woman who drove by and said she saw the teenager dragging a 12-year-old boy down a street. Lawyers for Black's family say he merely was playing with a longtime friend and wasn't harming the child.

Petyo, the police chief, said the woman who called 911 didn't know Black or the 12-year-old boy.

Webster told investigators he saw Black pin the 12-year-old against the hood of his patrol car, according to the statement from the state's attorney. Black identified himself as the 12-year-old's brother, but the body camera video shows the boy denying that.

The video then shows officers chase Black before he locked himself inside a car parked outside his family's home. An officer used a baton to break the driver's side window and then shocked Black with a Taser through the broken window before the teen got out and began struggling with the officers.

"Stop! You're under arrest!" an officer yelled.

The body camera footage shows Black's mother screaming her son's name as she sees officers pinning him down outside her home. One appears to lie on top of him as officers struggle to handcuff him.

"Anton, stop, baby!" she said after police handcuffed him.

"I love you!" he shouted.

"You'll be better if you don't fight. Calm down," a man said off camera.

"This is a mental health emergency. We're not treating this like a crime," an officer says. "He's not with us right now. He's going to be OK. We're going to get him some help."

The mother asks if her son will be locked up; an officer responds that they will instead take him to a hospital.

About 30 seconds later, the officers turned the handcuffed teen onto his back and checked for a pulse.

"He's breathing," a voice says.

The teen appears to be unresponsive. A dispatcher asks over the radio whether the teen is conscious and alert, and an officer replies, "Negative."

His mother points out that her son is "turning dark." Officers removed his handcuffs and began performing CPR on him. They also administer Narcan, meant to counter the effects of opioids. Black later was pronounced dead at a hospital.

The medical examiner's report says Black's medical record shows he recently had been involuntarily hospitalized and diagnosed with bipolar disorder. The report describes his mental illness as a "significant contributing condition." It doesn't show that drugs were in his system.

Maloney and Rene Swafford, another attorney representing the family, said they are conducting an independent review of forensic and medical evidence. "In any event, Anton Black did not die because of any mental condition," they said in a statement.

Webster was placed on administrative leave earlier this month. Petyo said Webster has returned to active duty following the decision by the state's attorney, but the chief said the officer isn't on a patrol assignment, in uniform, or interacting with the public.

Petyo said he will review the officer's status once the department receives official notice of the prosecutor's decision.